If part of your roof is shaded for part of the day, or your panels face different directions, standard string inverters force every panel to match the weakest performer. Solar panel optimisers fix this by giving each panel its own maximum power point tracker.
Solar panel optimisers recover 3-18% of lost energy depending on shading severity. NREL testing shows 3-4.5% gains under light shading and 15-18% under moderate shading compared to a standard string inverter. On mixed-orientation roofs (east/west split or multi-angle), optimisers recover 10-15% of production that would otherwise be lost to mismatch.
Solar panel optimisers are also known as solar PV optimisers or power optimisers. If you are also choosing panels, browse the UK solar panels directory.
Solar PV Optimisers and Shading
Shading is a common issue for solar panel owners, especially in urban environments or areas with tall trees. Even a small amount of shade on one panel can pull down the output of the whole string. Optimisers can reduce most of that loss.
NREL Shading Data: Energy Gains by Shading Level
The figures below come from the NREL Photovoltaic Shading Testbed and Tigo global dataset, comparing optimised strings against a standard string inverter:
| Shading Level | Optimiser Energy Gain vs String |
|---|---|
| Unshaded | 2.0-2.7% |
| Light shade | 3.0-4.5% |
| Moderate shade | 15.0-18.0% |
| Heavy shade | 18.0-22.0% |
| Mixed orientation | 10.0-15.0% |
How Solar Panel Optimisers Reduce Shading Losses
Consider a string of three solar panels, each rated at 40V and 5A. One panel gets partially shaded and drops to 35V and 4A, while the other two still produce 40V and 5A. Without optimisers, the entire string is pulled down to 4A and the voltage sum (35V + 40V + 40V). The two unshaded panels are forced to waste capacity.
Per-Panel Maximum Power Point
With solar panel optimisers, each panel operates at its Maximum Power Point (MPP) within the constraint of the 4A current. The optimisers adjust the voltage of the unaffected panels above 40V to get the most power possible at that reduced current. For a deeper look at which models perform best, see our best solar panel optimisers guide.
Solar Power Optimisers and Panel Orientation
When installing solar panels, it is not always possible to have all panels facing the same direction or at the same tilt angle. This can lead to different panels receiving different amounts of sunlight and producing different amounts of power. If you are deciding between a string inverter and microinverters, the inverter comparison guide covers that trade-off in detail.
With solar panel optimisers, each panel operates independently at its MPP regardless of its orientation. Panels facing east and west can sit on the same string without one direction dragging down the other. NREL data puts the production gain at 10-15% on a mixed-orientation roof compared to a standard string inverter.
Do Solar Power Optimisers Help on Cloudy Days?
Optimisers are good at reducing mismatch losses. When cloud cover is uniform across all panels, there is no mismatch to fix, so the optimiser adds little value and introduces a small conversion loss.
A study by the University of Southern Denmark found that under uniform cloudy conditions, optimisers slightly reduced efficiency: 99.3% and 98.9% for two brands tested, versus 100% for a modern string inverter. That 0.7-1.1% loss on overcast days is typically outweighed by gains on sunny days with any shading or orientation mismatch.
The net result depends on your specific roof:
- Expected number of cloudy days per year
- How uniform the cloud effect is across all panels
- Other partial string disruptions (chimneys, dormers, nearby trees)
The same study confirmed that optimisers are beneficial when mixing panels with different orientations.
How Solar Panel Power Optimisers Work
Solar power optimisers are compact electronic devices that attach to the back of a panel. They use the panel’s existing connectors as input and provide a second set of connectors as output to the next panel in the string. They sit between the panel and the string, managing each panel individually.
Solar power optimisers are DC/DC converters that adjust the voltage and current from a solar panel to maximise its output power. They continuously track each panel’s Maximum Power Point (MPP). Here is how they work:
- Voltage and Current Sensing: The optimiser continuously measures the voltage and current output of the solar panel.
- Maximum Power Point (MPP) Tracking: The optimiser calculates the MPP for that specific panel at that moment using these measurements.
- DC/DC Conversion: Once the MPP is identified, the optimiser adjusts the DC output using a buck-boost converter to align it with the MPP, keeping the panel at peak efficiency.
- Output to Inverter: The optimised DC output is then sent to the central inverter, where it is converted to AC for use in the home or grid.
- Communication: Many optimisers send performance data to a central monitoring system, allowing real-time tracking and troubleshooting.
Tigo shows in real time how much power you are getting from individual panels. - Safety Features: Some optimisers reduce the panel’s output voltage to a safe level when the inverter is off or during maintenance.
The Role of Maximum Power Point Tracking (MPPT)
Maximum Power Point Tracking (MPPT) at panel level matters because individual solar panels are affected differently by temperature, shading, and ageing. Here is how per-panel MPPT interacts with the rest of the string:
- Individual Panel Monitoring: Each optimiser continuously monitors its panel’s output and adjusts voltage and current to the MPP.
- String Aggregation: In a traditional string without optimisers, all panels are constrained by the weakest one. With optimisers, each panel operates independently at its MPP.
- Data Synchronisation: Optimisers communicate with the central inverter or monitoring system so the inverter operates at the global MPP for the entire string.
- Balanced Output: Because each panel operates at its MPP, the string produces a more consistent and higher output overall.
- Dynamic Adjustment: As conditions change (partial cloud cover, debris, or sun angle), the optimisers adjust each panel’s operating point to stay at the MPP throughout the day.
- Compatibility: Optimisers allow panels with different orientations, types, or ages to share the same string without reducing overall system performance.
Conclusion
Solar power optimisers are most useful when your roof has shading, mixed panel angles, or panels at different tilts. NREL data puts the gain at 3-4.5% under light shading and 15-18% under moderate shading. On a mixed-orientation roof, expect 10-15% more production compared to a plain string inverter. Uniform cloud cover is the one case where optimisers add little value. If you are calculating whether solar is worth it, see our solar panels worth it guide, and if you are choosing between optimisers and microinverters, the inverter comparison guide covers that decision.
